PURDUE UNIVERSITY COLLEGE OF VETERINARY MEDICINE EQUINE HEALTH UPDATE For Horse Owners and Veterinarians Vol. 21, Issue No. 2 – 2019 Navicular Disease By Brent Unruh, DVM Student (Class of 2020) Edited by Tim Lescun, BVSc, MS, PhD, Dipl . ACVS What is navicular disease? The navicular bone is a small bone present on the backside of the foot between the short pastern bone and the coffin bone . In a healthy horse, the navicular bone func- tions to equally distribute mechanical forces between the coffin (pedal) bone, short pastern bone and the deep digital flexor tendon (DDFT) . Therefore, navicular disease is the result of degenerative changes occurring within the navicular bone or with the soft tissue structures that make up the navicular apparatus . The navicular apparatus is comprised of the distal sesamoid impar ligament, the navicular suspensory ligament, the navicular bursa and the deep digital flexor tendon Figure( 1) . This disease is a com- Contents... mon cause of lameness in horses 4 to 15 years of age, encompassing roughly 30% of all Health lameness cases . Some will refer to navicular disease as a syndrome because the inciting Neonatal cause is unknown and it typically does not affect just one structure . The source of pain Isoerythrolysis . pg . 3 is multifactorial ranging from the bone itself to components of the navicular apparatus, Equine Recurrent or a combination of both . There are two main mechanisms that are believed to result in Uveitis . pg . 6 navicular disease: vascular compromise to the foot and biomechanical abnormalities . Navicular Disease . pg . 1 The most accepted mechanism is that biomechanical abnormalities of the foot alter the normal forces present on the navicular apparatus leading to tissue degeneration . News & Notes Alterations in the biomechanical forces can be due to poor conformation of the foot Research Update – and pastern, hoof imbalances, improper shoeing or trimming, excessive weight bearing Vitamin C and Sepsis . pg . 5 and exercise on hard surfaces . Who’s Who? . .pg . 2 Figure 1. Drawing of the normal anatomy of an equine foot. In Depth (https://www.cavallo-inc.com/wp- Equine Recurrent content/uploads/elementor/thumbs/ Uveitis . pg . 6 Hoof-Anatomy-ms4s03kqnax45 ytdfrzshbgkmhlyiszvaxsztz8vig.jpg) How do we diagnose it? Diagnosing navicular disease can be achieved using the clinical presentation, a thor- ough lameness exam and imaging modalities . Horses suffering from navicular disease typically present with a progressive, bilateral forelimb lameness resulting in decreased performance, stiffness, short strides and an unwillingness to make short turns . On lameness exam, these horses may exhibit sensitivity over the frog of the foot when hoof Visit vet.purdue.edu/ePubs testers are applied . Specific lameness tests and nerve blocks can be performed to further for more information on how localize the origin of pain to the heel region . However, the anatomy of the equine foot to access the newsletter through is complex, so diagnosis of navicular disease must include imaging such as radiographs . our PVM ePubs app. (continued on page 2) News & Notes Dr. Jenni Auvinen is originally from a My name is Ahmed Khairoun . I was small town in Finland where she grew up a senior clinician at the American Fon- spending all her free time at a local riding douk Working Equid Hospital in Fez, school . At an early age, she started groom- Morocco before I had an offer to start ing show jumpers, and after graduating my Large Animal Surgery Residency at from high school she continued to work Purdue University . My ultimate goal is as a groom in Finland and internationally . to become a surgeon to bring these skills Ever so eager to learn more, Dr . Auvinen back to Morocco in order to teach the returned to Finland to undertake a one- next generation of Moroccan equine vets . year horse massage course near home before starting her veterinary I am happy to know that I can use my knowledge to save equine education in the United Kingdom . Dr . Auvinen graduated with lives, improve human livelihoods and improve equine surgery honours from the University of Nottingham, School of Veterinary capability in my country . Medicine and Science, and moved to Canada to join the Moore I studied veterinary medicine at the IAV in Rabat, Morocco Equine Veterinary Centre as an intern veterinarian . Following her and after that I completed 4 equine internships . The first was at internship by the Rocky Mountains, she once again followed her the American Fondouk in Fez, Morocco, the second was completed dream and relocated to Indiana to start her Large Animal Internal at the University of Lyon, France, the third was in private equine Medicine training program at Purdue University in the summer surgical practice at Milton Equine Hospital in Canada and my last of 2019 . Dr . Auvinen has a soft spot for foals and other neonates one was at Purdue University . During my internships on these 3 as well as naughty ponies . Her main areas of interest include neo- different continents, I have realized that each presents different natology, cardiovascular diseases, gastroenterology and endocrine challenges and I continue to learn a wide array of procedures . disorders . In her sparse free time, Dr . Auvinen enjoys riding horses Apart from equine surgery my main passion is playing vio- and reading books, as well as spending time outdoors . Her plan is lin, especially Andalusian music . Performing for people is a truly to explore the States with friends and family visiting from home . lovely feeling . Navicular Disease (continued from cover) Advanced imaging, which includes ultrasound, computed Figure 2. An MRI image tomography (CT) and magnetic resonance imaging (MRI), showing abnormalities within is highly encouraged . MRI is the gold standard as it allows a the navicular bone. (https:// www.yourhorse.co.uk/advice/ more accurate assessment of bone and soft tissue structures of vet-advice/articles/2016/4/19/ the foot (Figure 2) . navicular-syndrome) How do we treat it? There is not a gold standard treatment for navicular disease, as it is not curable . Instead, the treatment centers around managing the level of pain present through multiple, different techniques, such as medical or surgical therapy . to choose the most appropriate type of shoes to restore balance Medical Management to the foot and reduce biomechanical forces on the navicular Medical management of navicular disease encompasses three apparatus . Common shoe types utilized in navicular patients major methods: rest and controlled exercise, corrective trim- include, but are not limited to, regular shoes with heel elevation ming and shoeing, and systemic and local medications . Al- and egg-bar shoes (Figure 3 & 4) . Shoes with heel elevation though rest is important, it is recommended that stall rest be decrease the tension placed on the DDFT to allow better weight utilized for 3 weeks followed by 3 weeks of controlled exercise, distribution and reduce the pressure applied to the navicular such as walking . This period typically follows corrective shoeing apparatus . The main disadvantage to this shoe type is that it allowing the horse to adjust to wearing the shoes and inflamma- slows heel growth, making patient selection an important factor . tion in the navicular apparatus to subside . The method of cor- Egg-bar shoes are not as effective as heel elevation shoes, but are rective trimming and shoeing of horses with navicular disease useful in patients with underrun heels because they help redis- is crucial for the management of pain . It is imperative that the tribute weight across the sole of the foot . Systemic medications veterinarian and farrier utilize the available imaging modalities should be utilized in addition to other management techniques 2 (continued on page 4) Neonatal Isoerythrolysis (NI) – Why Blood Typing Can Be Important By Hannah Clinton, DVM Student (Class of 2020) – Edited by Sandra D . Taylor, DVM, PhD, Dipl . ACVIM-LA Just like a person may be “A positive” or “O negative” with dam’s antibodies from the gut into the blood, which subse- respect to blood type, horses have varying blood types as well . quently leads to destruction (lysis) of the foal’s red blood cells, There are many different red blood cell antigens (factors) that causing hemolytic anemia . determine a horse’s blood type, but the Aa and the Qa antigens A foal with NI will seem healthy at the time of foaling, have the potential to cause the biggest reactions . While a horse’s but will become lethargic and depressed within the first 2-4 blood type is important when it comes to blood transfusions, days of life . The foal’s mucous membranes and sclera (whites of it is also important in the realm of reproduction . the eyes) will appear icteric (yellow/jaundiced) due to pigment If a mare does not have the Aa antigen, but the stallion accumulation from the red blood cell destruction (Figures 1 does, the foal is at risk for developing a hemolytic blood dis- and 2) . How rapidly the disease progresses depends on the red order known as neonatal isoerythrolysis, or NI . NI is very rare blood cell antigen (Aa or Qa) and the severity of the red blood and only occurs 1-2% of the time, but it is life-threatening when cell destruction . Seeking treatment as quickly as possible is it happens . For NI to occur, the foal would have inherited the necessary to save the foal’s life . sire’s dominant Aa positive blood type and, during gestation, Most veterinarians will diagnose this disease based on the mare will be exposed to the foal’s blood, which is recognized the history of a multiparous mare with a foal that develops by the mare’s body as a foreign substance . The mare will then clinical signs (jaundice, weakness, depression) within a few develop antibodies towards the foal’s blood .